1. Field of the Invention
This disclosure relates to compositions for servicing a wellbore. More specifically, this disclosure relates to methods of preparing storable nonaqueous cement slurries and the use of same.
2. Background of the Invention
A natural resource such as oil or gas residing in a subterranean formation can be recovered by drilling a well into the formation. The subterranean formation is usually isolated from other formations using a technique known as well cementing. In particular, a wellbore is typically drilled down to the subterranean formation while circulating a drilling fluid trough the wellbore. After the drilling is terminated, a string of pipe, e.g., casing, is run in the wellbore. Primary cementing is then usually performed whereby a cement slurry is pumped down through the string of pipe and into the annuals between the string of pipe and the walls of the wellbore to allow the cement slurry to set into an impermeable cement column and thereby seal the annulus. Subsequent secondary cementing operations, i.e., any cementing operation after the primary cementing operation, may also be performed. One example of a secondary cementing operation is squeeze cementing whereby a cement slurry is forced under pressure to areas of lost integrity in the annulus to seal off those areas.
These cementing operations may employ the use of storable aqueous cement slurries retarded to remain pumpable over extended time periods. While these slurries have many advantages they hold several potential drawbacks. In particular, one of the problems encountered with such slurries is the higher cost of transporting the slurry to locations considering the relatively high ratio of water to cement which can be contrasted to the costs incurred with transport of dry cement blends and on-site mixing with water. The most direct way to address these issues would require increasing the amount of cement in these slurries, however, the resulting viscosity increase would render the slurry unpumpable. An additional drawback to the use of such slurries is although they are formulated for extended storage, the duration of storage is limited. Over time the water in the slurries hydrates the cementitious material resulting in adverse advents such as gellation. Thus, a need exists for a storable cement slurry having a decreased liquid to cement ratio with an extended shelf life